1. Field of the Invention
The present invention relates to an image forming apparatus which comprises a detection unit which detects a reflected light amount from a measurement image.
2. Description of the Related Art
Conventionally, in image forming apparatuses that use an electrophotographic image formation process, variation easily occurs in the image density due to various conditions such as the usage environment and number of printed sheets. In particular, in color image forming apparatuses that perform color printing by overlaying toner images of multiple colors, variation occurs in the color balance (so-called color tone) if variation occurs in the image densities of the various colors, and therefore the suppression of density variation has been an important issue.
In recent years, in image forming apparatuses, a measurement image is formed on a transfer member carrier, the measurement image is measured by an optical sensor, and image formation conditions such as the exposure amount and developing bias are controlled based on the results of the measurement. In the case of measuring toner, measurement is performed using the amount of change in the amounts of specular light and diffused light between when toner is present and not present. For example, in the case of measuring a measurement image formed using yellow, cyan, and magenta toner, the attached toner amount of the measurement image is detected based on the amount of diffused light from the measurement image. Also, in the case of measuring a measurement image formed using black toner, for example, the attached toner amount of the measurement image is detected based on specular light from the measurement image. In this case, if the optical sensor has a blot due to scattered toner in the image forming apparatus, the amount of emitted light and the amount of received light will decrease. The measurement precision of the optical sensor therefore decreases significantly.
The optical sensor is subjected to light emission amount adjustment before the measurement image is measured by the optical sensor. In the light emission amount adjustment performed on the optical sensor, reflected light from a region of the image carrier not having toner attached thereto (base region) is measured by the optical sensor, and the light emission amount is adjusted such that the measured value matches a predetermined value. Also, in the case of an optical sensor that measures both the amount of specular light and the amount of diffused light, the light emission amount is set such that the amount of specular light from the base region is lower than a threshold value, and furthermore the amount of diffused light from the measurement image is lower than a threshold value (Japanese Patent Laid-Open No. 2000-338730).
The specular light from the base region and the diffused light from the measurement image change depending on the apparatus configuration, the wear of the image carrier, and the like. For this reason, if the light emission amount is determined based on either the amount of specular light from the base region or the amount of diffused light from the measurement image, and then the amount of received light based on the other one exceeds the threshold value, re-adjustment needs to be performed (see Japanese Patent Laid-Open No. 2004-117807).
However, conventional techniques have the problem that a long amount of time is required for adjusting the light emission amount. Furthermore, since a measurement image is formed in order to carry out light emission amount adjustment, there is the problem that toner is consumed. Also, if the change in the amount of specular light is caused by scratching or blotting on the base region in addition to blotting on the optical sensor, it is possible for a change to occur in the characteristics of the light emission amount and the amount of diffused light, and the characteristics of the toner density and the light emission amount. For this reason, there is also the possibility of not being able to set an appropriate light emission amount according to which the amount of specular light and the amount of diffused light do not exceed the threshold values.
In light of the above circumstances, according to an aspect of the present invention, downtime is suppressed when executing light emission amount adjustment on the optical sensor, and the amount of toner consumed due to the light emission amount adjustment is reduced.